1. Field of the Invention
The present invention relates to an image stabilizer for correcting an image blur due to hand-held shooting, and an optical instrument therewith.
2. Description Related to the Prior Art
Many optical instruments including digital still cameras have an image stabilizer or a shake correction device for correcting an image blur caused by vibration or a camera shake due to hand-held shooting. The image stabilizer is constituted of a shake detector for detecting the camera shake, a holder for movably holding an optical element such as a taking lens or an image sensor, a computing unit, an actuator for shifting the holder in a plane where the optical element is orthogonal to a photography optical axis, and a position detector for detecting the position of the optical element. The computing unit calculates which direction and how much the optical element should be shifted, based on a detection result of the shake detector such as an angular velocity sensor. The actuator performs feedback control of the position of the optical element during the camera shake, by using a calculated shift amount as a target value and a present position detected by the position detector as a measurement value.
In some conventional image stabilizers, the layout of the actuator and the position detector is devised for downsizing. According to ENOMOTO (Japanese Patent Laid-Open Publication No. 11-015037), for example, the center of an air-core coil, which is a part of the actuator, coincides with the photography optical axis. In TAKEDA (Japanese Patent Laid-Open Publication No. 2000-199920), an inner support frame slidably supports a lens frame having a shake correction lens for horizontal movement via guide shafts. An outer support frame supports the inner support frame slidably in a vertical direction via guide shafts. Linear motors as the actuator and position detection sensors as the position detector are disposed between the lens frame and the inner support frame and between the inner support frame and the outer support frame. If the linear motors are turned off while the camera shake does not occur, X-axial and Y-axial springs are provided in order to keep the optical axis of the shake correction lens aligned with the photography optical axis.
SHIN et al. (U.S. Patent Application Publication No. 2006/0132613 corresponding to Japanese Patent Laid-Open Publication No. 2006-171694) discloses an image stabilizer that shifts an image sensor in response to the camera shake for preventing occurrence of the image blur. The image stabilizer has a first frame that is slidably supported by a pair of X-axis guide shafts and a second frame that is slidable in a Y-axis direction on the first frame. The second frame holds the image sensor, and is slidably supported by a pair of Y-axis guide shafts attached to the first frame. The first frame is equipped with a linear motor, and the second frame is equipped with a voice coil motor. The linear motor and voice coil motor are disposed adjacently to each other. According to OKUMA (Japanese Patent Laid-Open Publication No. 2007-148023), a lens barrel contains a magnetic material or has a magnetic layer on its surface to function as a yoke.
In the foregoing prior art, each of the X-axis and Y-axis sliders or frames is slidably supported by a pair of guide shafts. This structure is the main impediment to downsizing of the image stabilizer. ENOMOTO and SHIN et al. have limited flexibility in the coil layout, and there are cases where the image stabilizer is difficult to downsize anymore. TAKEDA has the problem of wobble that occurs between the guide shaft and a bearing of the slider. The wobble degrades precision of the position detector. It is conceivable to dispose a spring between the guide shaft and the bearing for reducing the wobble, but friction of the spring lowers the followability of the holder to the actuator.